4. Correct Answer: D. Target sign in the RLQ
Rationale: Abdominal pain is one of the most common complaints in the ED and there is a concern for the overuse of ionizing radiation with CT scans. For this reason, the American College of Emergency Physicians and American College of Radiology recommend ultrasonography (US) as the initial radiologic modality for evaluation of acute appendicitis (AA), especially in the pediatric population. Ultrasound is less sensitive than CT (˜86%), but the specificity is high (˜95%).
The diagnosis of AA can be achieved by direct visualization of the appendix or indirectly by observing signs of local inflammation. Direct signs include noncompressibility of the appendix (except in the case of perforation), a diameter >6 mm, wall thickness ≥3 mm, visualized appendicolith (hyperechoic structure with posterior shadowing), enhanced vascularity (seen in early stages of AA) or decreased/absent vascularity (seen with abscess and necrosis), or the presence of a “target sign.” The target sign is described as a hypoechoic fluid-filled center surrounded by hyperechoic mucosa/submucosa, surrounded by a hypoechoic muscularis ring. Indirect signs of AA are free fluid surrounding the appendix, local abscess formation, increased echogenicity of adjacent mesenteric fat, enlarged mesenteric lymph nodes, thickening or hyperechogenicity of the peritoneum, and signs of secondary SBO.
1. Benabbas R, Hanna M, Shah J, Sinert R. Diagnostic accuracy of history, physical examination, laboratory tests, and point-of-care ultrasound for pediatric acute appendicitis in the emergency department: a systematic review and meta-analysis. Acad Emerg Med. 2017;24(5):523-551. doi:10.1111/acem.13181.
2. Mostbeck G, Adam EJ, Nielsen MB, et al. How to diagnose acute appendicitis: ultrasound first. Insights Imaging. 2016;7(2):255-263. doi:10.1007/s13244-016-0469-6.
3. Noguchi T, Yoshimitsu K, Yoshida M. Periappendiceal hyperechoic structure on sonography. J Ultrasound Med. 2005;24(3):323-327. doi:10.7863/jum.2005.24.3.323.
4. Quigley AJ, Stafrace S. Ultrasound assessment of acute appendicitis in paediatric patients: methodology and pictorial overview of findings seen. Insights Imaging. 2013;4(6):741-751. doi:10.1007/s13244-013-0275-3.
5. Smith EA, Smith WL. Pediatric imaging. In: Farrell TA, ed. Radiology 101. Wolters Kluwer; 2020:144-174.